Remove docstrings for doc_filter parameters

[atravitz]

from TODO:

signac/signac/contrib/project.py

Line 75 in dac2c30

# TODO: In signac 2.0, remove all docstrings for doc_filter parameters. The

we are removing doc_filter from the API in 2.0.

[vyasr]

After numerous discussions, we are instead planning to remove the doc filter entirely in signac 2.0. This is done in #752, so this issue can be closed (we'll have to do a final pass over all our docstrings before releasing 2.0 to make sure that everything has been appropriately updated).